3com 8807 User Guide

PW signaling (pseudowire signaling) protocol on which VPLS bases is used to 
establish and maintain PW. It can also be used to automatically discover peer PEs 
of VSIs. Currently, PW signaling protocol includes label distribution protocol (LDP) 
and border gateway protocol (BGP).

Service quality maps priority information in the headers of user’s layer 2 packets 
and QoS information carried by VSI instances to QoS priority of the public network 
before the forwarding of the packets. This feature generally requires the MPLS 
network to support traffic-engineering.

As shown in Figure 154, CE3 transmits uplink layer 2 packets to PE1 through AC. 
When PE1 receives the packets, the forwarder chooses PW to forward them. 
According to PW forwarding entries, the system generates two layers of MPLS 
labels (private network labels are used to mark the PWs, and public network labels 
are used to pass through tunnels to PE2) and the Ethernet headers of the public 
network. After the packets reach PE2 through public network tunnel, the system 
pops out private network labels (public network labels have already been popped 
out on P device through PHP). PE2 forwarder chooses an AC to forward layer 2 
packets from CE3 to CE1.

An MPLS L2VPN is a VPN that transparently transmits user’s layer 2 packets over 
MPLS network. In user’s perspective, an MPLS network is a layer 2 switching 
network, over which layer 2 connections can be set up among different sites. 
MPLS L2VPN includes VLL and VPLS.

This is a kind of point-to-multipoint L2VPN service provided on public networks. 
VPLS can connect user sites in different areas together over MAN/WAN as if they 
are in a single LAN.

This is a kind of point-to-point L2VPN service provided on public networks. VLL 
can connect two sites with each other as if they are directly connected by cables. 
However, it cannot provide switching directly between multiple points at the 
service provider level.

It is a user device that is directly connected with a service provider’s device.

It is an edge router in backbone network connected with CEs. PE is responsible for 
VPN service access, it implement packet mapping and forwarding from private 
networks to public network tunnels, and vice versa. It has two types: UPE and NPE.

It is a user-facing PE device, a kind of convergence device for users to access the 
VPN.